1. Field of the Invention
The invention relates to a power assist devide for amplifying force from a control signal, particularly as used in marine control systems.
2. Prior Art
In a marine control system for throttle and clutch controls of a vessel it is usual to have several control heads located in various parts of the vessel, for example on the bridge, at the stern and in the engine room. These controls are integrated into a common control signal receiver which then transmits the control signal to the engine, clutch, etc. The various control heads interconnect with the control signal receiver by push-pull cables, tensioned cables, etc. and, in the larger vessels, a considerable length of cable is used, the cable often being subjected to bends to negotiate obstructions. Friction losses in the cable increase with the length of cable and the number of bends, and in some applications considerable force is required at the control head to overcome friction in the cable system to actuate the controls. Excessive friction contributes to loss of sensitivity or "feel" of the controls and it can be difficult to locate a desired setting or datum at the apparatus being controlled, for example it can be difficult to locate the neutral position on a gear box, or a selected throttle position.
In the past, power assist devices have been coupled to control systems to reduce the effects of friction at the control head, and, whilst applied force necessary to operate the controls has been reduced by these devices, loss of "feel" or sensitivity of the controls has resulted, further compounding the difficulty of locating a desired setting, for example neutral. Various devices have been developed to provide feel in power assist control systems, but to the applicant's knowledge, these devices have not provided positive feel for selected positions in such control systems.
A related device is shown in U.S. Pat. No. 3,202,011 issued in 1965 to the present inventor. When compared to the present invention, this patented device has several limitations, one of which is that it is adapted only for clutch control, and not combined clutch and throttle control as in the present invention.